Structural Characterization of CeO₂−MO₂ (M = Si⁴⁺, Ti⁴⁺, and Zr⁴⁺) Mixed Oxides by Raman Spectroscopy, X-ray Photoelectron Spectroscopy, and Other Techniques

Abstract

Microstructure evolution of ceria-based mixed oxides CeO2−MO2 (M = Si4+, Ti4+, and Zr4+) after thermal treatments in the temperature range of 773−1073 K were investigated by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and other techniques. The CeO2−SiO2 was synthesized by a deposition precipitation method, and a coprecipitation procedure was adopted to make CeO2−TiO2 and CeO2−ZrO2 binary oxides. The XRD measurements revealed the presence of crystalline cubic CeO2 on the surface of SiO2 in CeO2−SiO2, CeO2 and TiO2 (anatase) in CeO2−TiO2, and Ce0.75Zr0.25O2 and Ce0.6Zr0.4O2 phases in CeO2−ZrO2 samples. The crystallinity of these phases increased as the calcination temperature increased. Estimations of the cell parameter a indicated an expansion of the CeO2 lattice in the case of CeO2−TiO2 samples, whereas a contraction was noted in the case of CeO2−ZrO2. Some incorporation of Si4+ ions into the CeO2 lattice was noted at higher calcination temperatures for the CeO2−SiO2 samples. Raman measurements revealed the presence of oxygen vacancies, lattice defects, and the displacement of oxide ions from their normal lattice positions in the case of the CeO2−TiO2 and CeO2−ZrO2 samples. The XPS studies revealed the presence of silica, titania, and zirconia in their highest oxidation statesSi4+, Ti4+, and Zr4+at the surface of the materials. Cerium is present in both Ce4+ and Ce3+ oxidation states, but in different proportions, depending on the mixed-oxide system and the calcination temperature used.

WGS and CO-PrOx reactions using gold promoted copper-ceria catalysts: “Bulk CuO CeO2 vs. CuO CeO2/Al2O3 with low mixed oxide content”

“…Figure 2A shows the Raman spectra of the prepared CuCe catalysts. All samples exhibit a main band centered at about 462 cm −1 , which is assigned to Ce F2g mode due to symmetrical stretching of Ce-O vibrational unit in octahedral coordination [40,41]. As reported by Graham et al [42], broadening and shifting of this band indicates variations in ceria particle size.…”

“…Raman spectroscopy of fluorite type oxide structures are dominated by oxygen lattice vibrations, which are sensitive to the crystal symmetry, thus being a potential tool to obtain additional structural information [40]. Indeed, interesting differences between the bulk CuO-CeO2 and the supported CuO-CeO2/Al2O3 samples can be established from the Raman study.…”

Preferential oxidation of CO in excess of H2 on Pt/CeO2–Nb2O5 catalysts

“…The Raman spectrum of pure ceria exhibits a main peak at 462.9 cm -1 , which is assigned to F 2g mode due to symmetrical stretching of Ce-O vibrational unit in eightfold coordination [23][24][25]. It is interesting to note the decrease of the intensity of this band with an increase of the niobia content.…”

Structure-activity Relation of Fe2O3–CeO2 Composite Catalysts in CO Oxidation

“…A general method to increase the thermal stability and OSC of CeO 2 during operations is to introduce other metal ions into the ceria cubic fluorite structure [2,3,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. This approach offers an opportunity not only to improve the performance of the involved metal oxide but also to form new stable compounds that lead to totally different physical and chemical properties.…”